DESCRIPTION (Verbatim from Applicant's Abstract): Vasospasm contributes to vein graft spasm during vascular reconstructive surgery, non-occlusive mesenteric ischemia' Raynaud's syndrome, and cerebral ischemia after subarachnoid hemorrhage. Our understanding of the pathophysiology of vasospasm is limited, largely due to a lack of good models. However, a fundamental principal of vasospasm is that the vascular smooth muscle is refractory to relaxation. We have determined that cyclic nucleotide-dependent relaxation is associated with increases in the phosphorylation of the small heat shock-related protein, HSP20. We have developed a physiologic model of vasospasm, umbilical artery smooth muscle, which is uniquely refractory to relaxation and in this muscle, HSP20 is not phosphorylated. Another, closely related heat shock protein, HSP27,is highly expressed in muscle and is induced by stress. Elevated levels of phosphorylated HSP27 are associated with impaired relaxation and phosphorylation of HSP20, suggesting that phosphorylated HSP27 modulates contractile function by inhibiting the phosphorylation of HSP20. Both HSP27 and HSP20 are actin binding proteins and may modulate smooth muscle relaxation by a direct interaction with actin or with actin associated proteins. Thus, we hypothesize that HSP20 and HSP27 co-ordinately regulate the intrinsic tone of smooth muscle and this regulation is dependent on the phosphorylation and macromolecular associations of the two small heat shock proteins. The specific aims of this investigation are to: 1. Characterize the interactions of HSP20 with the smooth muscle contractile apparatus and determine the role these interactions in mediating vasorelaxation. 2. Determine the mechanisms by which phosphorylated HSP27 inhibits the phosphorylation of HSP20 and muscle relaxation. These studies will elucidate the molecular mechanisms of cyclic nucleotide-dependent relaxation and vasospasm due to impaired relaxation and may lead to more direct pharmacologic approaches to the treatment of vasospastic disorders.